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This article reports the electrochemical studies of bio-electrocatalytic oxygen reduction reaction catalyzed by a new laccase from a thermophilic bacterium, which exhibits superior stability and activity retention compared to fungal laccases. The electro-kinetic study of this catalytic reaction was conducted using a classic tool of electrochemistry, the rotating ring disk electrode (RRDE). Bacillus sp. FNT laccase was immobilized onto a multiwall carbon nanotube modified glassy carbon disk electrode using a molecular tethering agent, 1-pyrenebutanoic acid succinimidyl ester (PBSE). The conditions for laccase immobilization were optimized to prepare a highly active bioconjugate for the electrochemical reduction of oxygen. The kinetic parameters such as Tafel slopes, number of electrons transferred, electrochemical rate constant and the electron transfer rate were calculated from RRDE measurements. The rate constant of the four-electron transfer reaction was calculated to be 3.21 x 10(-1) +/- 8.5 x 10(-3) cm s(-1). The slope value obtained from Tafel plot was close to that of value for the ideal four-electron transfer oxygen reduction, suggesting excellent electro-catalytic activity of the FNT laccase-MWCNT conjugates. (C) 2018 The Electrochemical Society.

Development of efficient non-precious metals catalysts for the oxygen reduction reaction (ORR) has attracted considerable attention. A composite catalyst based on nickel- 5,10,15,20-tetra(p-thioanisole) porphyrin complex (Ni-TPT-P) and carbon fibres (CF) is here investigated for the ORR. The porphyrin is synthesised by a one-pot multi-step approach. Ultraviolet-visible (UV–vis) and fourier-transform infrared (FTIR) techniques are used to confirm the synthesis of the Ni-TPT-P complex. The metalloporphyrins (Ni-TPT-P) are non-covalently adsorbed on the CF via π − π stacking interaction. The composite catalyst shows well-defined redox peaks attributed to the Ni2+/Ni3+ redox couple in O2-saturated 0.1 M KOH solution. The area under the reduction peak is used to calculate a surface coverage ( Г ) of 2.43 × 1015 for the Ni2+/Ni3+ species on the catalyst surface area. The rotating ring disk electrode (RRDE) technique is used to assess the performance of the catalyst towards the ORR. Key performance indicators such as the onset potential, average number of electrons and HO 2 − yield are found to be, 0.82 V vs RHE, 3.6 electrons and 22.0% respectively.

Monodispersed TiN nanoparticles with a narrow size distribution (7–23 nm) were synthesized using mesoporous graphitic (mpg)-C3N4 templates with different pore sizes. The nano-materials were examined as electrocatalysts for oxygen reduction reaction (ORR) in alkaline media. The TiN nanoparticles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 sorption, transmission electron microscopy (TEM), and C-H-N elemental analysis. The ORR current increased as the TiN particle size decreased, and hence the surface area of TiN nanoparticles reactive to ORR increased. Rotating ring disk electrode (RRDE) measurements revealed that the ORR on TiN surfaces proceeded mainly via a two-electron pathway, producing H2O2 as the main product. Mechanistic aspects of ORR on TiN surfaces are discussed.

In situ rotating ring disk electrode (RRDE) and simultaneous electrochemical-electron spin resonance (SEESR) techniques have been employed to characterize the products and the phases of the products formed during voltammetric reduction or oxidation of microcrystalline solids mechanically attached to an electrode which has been placed in a solvent (electrolyte) medium in which the components are insoluble. Results obtained for reduction of solid organic 7,7,8,8-tetracyanoquinodimethane (TCNQ) and oxidation of solid organometallic trans-Cr(CO) 2 (dpe) 2 [dpe: 1,2-bis(diphenylphosphino)ethane)] show that the two compounds exhibit similar mechanistic pathways despite their substantially different chemical and physical natures. Data obtained from both RRDE and SEESR techniques show that a solid-state nucleation/growth mechanism confined to the electrode surface dominates the electrochemical processes at potentials where voltammmetric peaks are observed. Thus, for example, in solvent (electrolyte) combinations where the product of electrolysis ([TCNQ] - and trans-[Cr(CO) 2 (dpe) 2 ] + ) are insoluble, characteristic solid-state electron spin resonance (ESR) spectra are obtained. In contrast, solution phase ESR spectra are obtained when the electrode is placed in media in which the products are soluble. Data obtained confirm that the conductivity associated with the solids does not play a significant role in the voltammetric response of solid microcrystalline compounds when mechanically attached to an electrode surface

Early stages of aniline oxidation have been studied employing spectroelectrochemical and rotating ring disk electrode experiments in solutions of low (2 mM) and high (100 mM) aniline concentrations in . Results indicate that a large amount of the tail‐to‐tail dimer, benzidine, is produced in the initial stage of aniline oxidation, which is followed by the generation of the head‐to‐tail dimer, N‐phenyl‐p‐phenylene diamine (PPD), as well as oligomers in solutions of high aniline concentrations. The intermediate species have been identified by spectroelectrochemical and rotating ring disk electrode (RRDE) voltammetry experiments, and the relative amount of dimeric products has been estimated from the RRDE voltammograms. Evidence for the presence of a nascent species produced upon oxidation of aniline is presented from the RRDE experiments.

Formic acid formed on a SnO{sub 2} disk electrode as a reduction product of carbon dioxide was detected at a Pt ring electrode, and the fixation mechanism of carbon dioxide was investigated. It was found that organic products such as HCOOH could be detected electrochemically by a rotating ring-disk electrode technique which does not require a long-term electreoreduction and offers a much more sensitive method than gas and liquid-chromatography do. It was clarified that CO{sub 2} was reduced to HCOOH on the SnO{sub 2} surface in competition with hydrogen formation: both HCOOH and H{sub 2} were formed quite slowly in a few seconds. The rotational speed dependence of the reaction current revealed that a considerably slow electron transfer results in the formation of some intermediates, from which HCOOH will be formed under the mass-transfer-limited condition of proton. The formation of HCOOH was found to be most pronounced at pH 3.5.

The investigation of the anodic oxidation of iron in alkaline solutions is important because it is used as a cathodic reaction in Fe/Ni and Fe/air batteries, and it is also related to the corrosion of iron. The electrochemical oxidation of iron has been studied in concentrated alkaline solutions employing rotating ring-disk electrode voltammetric and in situ spectroelectrochemical techniques. While four anodic and cathodic cyclic voltammetric (CV) peaks may be observed at times, three cathodic CV peaks and four anodic peaks are observed under the usual experimental conditions. Results obtained from these studies are consistent with the conclusion that iron is oxidized to Fe(2) at the least positive anodic CV peak, Fe[sub 3]O[sub 4] at the second peak, [delta]-FeOOH and Fe[sub 2]O[sub 3] at the third peak, and Fe[sub 3]O[sub 4] below the [delta]-FeOOH layer at the most positive anodic peak. Corresponding cathodic CV peaks were identified for all these anodic processes, except for the most positive one. Evidence supporting the conclusion and detailed mechanisms for the iron oxidation is presented.

The electrodissolution behavior of Cu and Cu-rich Cu-Zn alloys in 1m HCl containing benzotriazole (BTA) was studied using rotating ring-disk electrodes. Cu(I) was the main product of Cu-Zn alloy dissolution with Cu(II) detected only at higher potentials. Electrodissolution of the Cu component was similar to that of copper with an apparent Tafel slope of 60 mV/dec. Cu component dissolution rates exhibited strong mass-transfer effects in the entire potential range studied

The electrodissolution kinetics of Cu-S Ni, Cu-10 Ni, and Cu-30 Ni alloys in acidic chloride solutions have been investigated with rotating ring-disk electrodes at various anodic potentials, H + and Cl - concentrations, and rotation rates. The kinetics and mechanisms of electrodissolution of the Cu component for all three alloys are consistent with results obtained previously for Cu. Electrodissolution of the Cu component exhibitied mixed mass-transfer and kinetic control in the apparent Tafel region and mass-transfer control in the limiting current region with cuprous chloride complex indicated as the limiting diffusion species. At potentials above the limiting diffusion current region, formation rates of Cu(I) and Cu(II) were under mass-transfer and kinetic control, respectively

The underpotential deposition of copper on Au(111) single-crystal substrate was studied using voltammetric and rotating ring-disk electrode measurements (RRDE) in sulfuric acid solutions of different Cu 2+ concentrations (5.10 4 ≤ c cu2+ ≤5.10 -2 mol liter -1 ) at constant pH 1 and T=298 K. Cyclic voltammograms and charge isotherms indicate that ideal metal-monolayer model, characterized by an electrosorption valency value of γ=z=2, is valid only at high degree of Cu ad coverage at low underpotentials. Significant deviation from the ideal behavior was observed at high underpotentials, where the electrosorption valency was found to be γ≃1

Rotating Pt-ring TiO 2 -disk electrodes were used to investigate the catalytic mechanism of Pt sites in platinized semiconductor catalysts. When a TiO 2 disk electrode immersed in a methanol-water mixture was illuminated with chopped light, an anodic current was observed at the Pt ring electrode even at cathodic potentials at which reduction (cathodic) current was expected to flow. This peculiar phenomenon was enhanced by oxygen bubbling and could be observed only in solutions with pH

The hydrodynamically square wave modulated rotating ring-disk electrode can be used for the investigation of electrochemical processes even under conditions for which the ring current is normally masked by a large background current. After stepping of the rotation speed, relatively large changes of the ring current (spikes) are observed. An analytical expression was found to describe the maximum of the change of the collection efficiency when the ring current is independent of the angular velocity of the electrode for stationary (steady-state) conditions

The hydrodynamically square wave modulated rotating ring disk electrode can be used in the investigation of electrochemical processes of arbitrary nature and extremely small rates when the ring current is masked by electronic offsets and a contribution due to impurities in the bulk electrolyte. In the suggested method a rectangular stepping of the angular velocity of the electrode is introduced. It allows the determination of the partial disk current under investigation. An analytical expression was found to describe the maximum change of the collection efficiency when the disk current is of arbitrary nature and impurities are present in the bulk electrolyte

The anodic oxidation of cyanide ion is catalyzed by the addition of cuprous ion. Studies with a platinum‐platinum rotating ring‐disk electrode indicate that at the anode cyanocuprous ion is oxidized to adsorbed cyanocupric ion which then decomposes primarily by a heterogeneous quasi‐second‐order intracomplex redox reaction. The rate of this heterogeneous reaction increases roughly linearly with homogeneous cyanide concentration, indicating a fundamentally different reaction mechanism from the homogeneous decomposition of the tetracyanocupric ion. An analytic model has been developed to simulate the effect of the heterogeneous reaction on the rotating ring‐disk electrode system. This model reproduces adequately the collection efficiencies observed experimentally.

The anodic oxidation of telluride ions was studied in using mainly hydrodynamic voltammetry. Thermodynamic (Pourbaix) analyses predicted stepwise oxidation of Te2− to , Te0, , and finally . Consistent with this expectation, was detected as a intermediate product at the ring, both in the forward , and in the reverse electron transfer directions. Studies with authentic samples of in revealed that this species could be collected at the ring both in the oxidative (−0.80V vs. SCE) and in the reduction (−1.20V) modes. Consequently, comparison of the ring response at −0.80V and −1.20V with the disk current profiles in provided further confirmation for the electrochemical generation of the intermediate. Finally, further oxidation of Te0 to and was detected via cyclic and hydrodynamic voltammetry.

A new method has been developed for determining the composition of and alloys electrodeposited on a rotating disk electrode. The method makes use of a ring‐disk assembly combined with potentiodynamic or galvanostatic stripping voltammetry. According to the method the alloy is first deposited on the disk electrode and subsequently transferred to a stripping medium where it is anodically dissolved. During disk dissolution, Sn in the alloy dissolves in the +2 oxidation state and further oxidizes to Sn4+ on the ring electrode. The disk charge is proportional to the total amount of deposit while the ring charge is proportional to the total amount of Sn in the deposit. In addition to permitting composition determination, this method provides information about the phase structure of the electrodeposited alloy.

Theoretical rotating ring and disk electrodes voltammograms are discussed for a process consisting of two consecutive charge transfer steps under steady‐state conditions. The relationship between total disk current, , and ring current,, is examined. Plots of vs. the reciprocal of the square root of the rotation rate, , are classified into three cases depending on the reversibility of the second charge transfer step. Although the voltammograms of the disk electrode may be those of a single wave, a distorted s‐shape, or a well‐separated two step, the ratio is not affected by the kinetic parameters of the first charge transfer step, except for the number of electrons.

Carbon-supported palladium–polypyrrole Pd–PPy/C nanocomposite was synthesized by oxidative polymerization of pyrrole and reduction of palladiumII precursor salt in the presence of Vulcan XC-72R. The Pd–PPy/C composites were characterized by X-ray diffraction XRD, Fourier transform IR, X-ray photoelectron spectroscopy XPS, thermogravimetric analysis TGA, and transmission electron microscopy TEM techniques. The XRD analysis of Pd–PPy/C shows the formation of the face-centered cubic structure of Pd particles and the mean particle size calculated from TEM was 5.3 2.0 nm. The electrochemical stability of Pd–PPy/C was examined by cyclic voltammetry in an acid solution. The thermal stability and Pd loading in the composite was assessed using TGA. The introduction of Pd in the conducting PPy/C matrix gives better catalytic activity toward oxygen reduction with resistance to methanol oxidation. This was further elucidated by the XPS analysis showing d-band vacancy that is attributed to metal–polymer interaction. From the polarization studies, it is observed that even in the presence of methanol there is no significant cathodic shift in the half-wave potential, revealing that Pd–PPy/C is tolerant to methanol. Rotating ring disk electrode studies show that there is only a negligible quantity of hydrogen peroxide produced in the potential region where its production is expected to be high. This confirms that Pd–PPy/C catalyzes reduction of oxygen directly to water through a four-electron pathway.

This work presents the preparation and investigation of pyrolyzed cobalt-tetramethoxyphenylporphyrin (CoTMPP) supported by iron oxalate with and without sulfur as electrocatalysts for the oxygen reduction reaction (ORR) in acid media. A preparation method which needs no addition of carbon supports allows the structural investigation of the pyrolysis products by X-ray photoemission spectroscopy, Raman spectroscopy, and X-ray diffractometry without any interferences of a carbon support. Already with low metal loading, rotating ring disk electrode measurements reveal the high ORR activity and enhanced selectivity which are apparently caused by an increased number of catalytic centers and higher efficient ones due to a well developed porosity and a suitable molecular structure of the formed carbon. A thermogravimetric investigation of the pyrolysis process shows that the addition of sulfur to the precursor influences the carbonization of the porphyrin in a favorable way. It has been found that extended graphene layers present a particularly suitable matrix for highly active catalytic centers.

The velocity and pressure profiles in the electrolyte due to a rotating disk electrode are determined by solving the two-dimensional (2D) Navier-Stokes equations employing axial symmetry. Most applications in the literature employ a one-term approximation of the series solution to von Karman's one-dimensional (1D) model for the rotating disk electrode. In this work, the finite-element method is used to solve the model equations rigorously within an electrochemical cell of practical dimensions, and the results are compared with the one-term approximate solution and a complete solution to the ID model. The different hydrodynamic models are coupled with a mass-transport model for oxygen reduction reaction at the surface of the rotating ring disk electrode. The complete series solution is accurate to within four digits when compared to the 2D model, whereas the one-term approximation gives rise to an error as high as 4% in the limiting current values. Similar calculations on a ring disk electrode show that the one-term approximation underestimates the collection efficiency and the ratio of the ring and the disk currents of a sectioned electrode by 1-4%.

Scanning electrochemical microscopy (SECM), in the substrate generation-tip collection (SG-TC) mode, has been used to detect the cuprous ion Cu (aq) + intermediate formed during the course of electrodeposition of Cu metal from aqueous CuSO4 solution. Addition of chloride is confirmed to strongly stabilize the Cu (aq) + ion in aqueous solution and enhance the rate of Cu electrodeposition. This SECM method in the SG-TC mode offers an alternative to the rotating ring disk electrode (RRDE) technique for in situ studies on the effect of plating bath additives in metal electrodeposition. An attractive feature of the SECM relative to the RRDE method is that it allows qualitative aspects of the electrodeposition process to be studied in close proximity to the substrate in a simple and direct fashion using an inexpensive probe, and without the need for forced convection.

A cylindrical two-dimensional model based on the Nernst–Planck equations, the Navier–Stokes equation, and the continuity equation is used to simulate the oxygen reduction reaction in 0.5 M H2SO4 at a rotating ring disk electrode. Concentration distributions and a potential profile are obtained as a function of the axial and radial distances from the center of the electrode surface. Polarization curves are simulated to interpret experimental results by studying various reaction mechanisms, i.e., the four-electron-transfer reduction of oxygen, the two-electron-transfer reduction of oxygen, a combination of the above two reactions, mechanisms with reduction of peroxide to water, and/or the heterogeneous chemical decomposition of peroxide. Special attention is devoted to the effect of peroxide.

The poisoning of the oxygen-reduction reaction (ORR) by adsorbed sulfur-containing species was quantified for platinum fuel-cell materials using rotating ring disk electrode methodology. Electrodes of Pt on Vulcan carbon (Pt/VC) were contaminated by submersion in SO 2 -containing solutions. The initial sulfur coverage of the Pt was determined from the total charge consumed as the sulfur was oxidized from S° at 0.05 V (vs a reversible hydrogen electrode) to water-soluble sulfate (SO 2- 4 ) at >1.3 V. Electrodes were then evaluated for their ORR activity. Significant (33%) loss in Pt mass activity was measured when approximately 1.2% of the Pt surface had adsorbed the sulfur-containing species. Sulfur coverage of 14% caused a 95% loss in mass activity. When 37% of the Pt surface was covered with sulfur, the reaction pathway of the ORR on the Pt/VC catalyst changed from a 4-electron to 2-electron process reaction for peroxide, a reagent which can aggressively attack Nafion. We conclude that adsorbed sulfur is not removed under typical steady-state operating conditions of a proton exchange membrane fuel cell, so it will affect operation by decreasing mass activity of the catalysts and by enhancing formation of the deleterious H 2 O 2 by-product.

The carbon-supported nanoparticles of Pd–Co–M (M = Pt, Au, Ag) catalysts for direct methanol fuel cells (DMFCs) in a ratio of (70:20:10) were prepared through reverse microemulsion method. The X-ray diffraction (XRD) analysis showed well-defined reflections corresponding to a face centered cubic phase of palladium. From transmission electron microscopy analysis, the particle size after heat-treatment at 500°C was found to be approximately 20 nm, which was also confirmed by XRD analysis. Polarization data indicated Pd–Co–Pt to have better oxygen reduction reaction (ORR) activity than the other combinations with Ag and Au, in terms of shift in onset potential to a positive value of more than 100 mV and increased reduction current. The ORR kinetics on Pd–Co–Pt was analyzed by using rotating disk electrode to follow a 4 electron pathway, the order of the reaction being unity. The peroxide formation estimated from the rotating ring disk electrode measurements was found to be a negligibly small amount of 1.1%. An additional advantage observed with Pd–Co–Pt was its high methanol tolerance and ORR activity nearly equal to Pt.

This study reports the effects of HF on the voltammetric responses below 3 V (vs. Li/Li + ) in LiPF 6 solutions being widely used in rechargeable lithium-ion batteries (LIBs). During the first cathodic scan on a Pt electrode, two reduction peaks are observed between 3.0 and 1.5 V in LiPF 6 solutions irrespective of the solvents used. The reduction reactions are absent in LiBETI solutions but present after the addition of trace amount of HF. Thus, the reduction reactions in LiPF 6 solutions are due to the HF, an inevitable impurity of LiPF 6 solutions. Based on the results of the rotating disk electrode and the rotating ring disk electrode experiments, two reduction peaks are assigned to the hydrogen underpotential deposition and the hydrogen evolution reaction, respectively. HF reduction reactions forms a surface layer of which the main constituent is LiF. The surface layer suppresses the other reduction reactions otherwise occurring below 3.0 V. For example, the electrodeposition of metallic Mn, which takes place below 1.0 V in LiBETI solutions, is severely hampered in LiPF 6 solutions. The passivity by HF reduction is observed not only for a Pt electrode but also for a glassy carbon electrode.

This article concerns the efficient dioxygen (O 2 ) reduction by a novel catalytic system that is comprised of two catalysts: one for the electroreduction of O 2 through the two-electron process and the other for the subsequent chemical decomposition of hydrogen peroxide generated. Here we represent the combined catalytic system of cobalt phthalocyanines and manganese oxide (MnOOH). Each catalyst performs well independently, leading to the totally four-electron reduction of O 2 in alkaline media. This was confirmed from almost twofold increases of the cathodic current in cyclic voltammograms and the steady-state current in rotating ring disk electrode voltammograms, the collection efficiency and the number of electrons calculated from the Koutecky-Levich plot. As a consequence, it is concluded that this combined catalytic system works efficiently for the O 2 reduction.

The galvanostatic plating of Cu-Al alloy was examined at a platinum electrode in solutions of Cu + in the 60.0-40.0 mol % aluminum chloride-1-ethyl-3-methylimidazolium chloride room-temperature molten salt at 28°C using periodic-current plating techniques. The plating techniques that were investigated include pulse current, superimposed-pulse current, and reverse-pulse current. The composition of the clectrodeposited alloy was determined by using rotating ring-disk anodic linear sweep voltammetry. The electrodeposition of Cu-Al is complicated by the instability of the alloy in solutions containing Cu + . If alloy clectrodeposits are removed from cathodic protection while immersed in the plating bath, a condition that occurs during the pulse plating off-time, f off , Cu + in the plating solution oxidizes Al from the electrodeposits. The rate of this displacement reaction is greatest for small values of t off but decreases as t off becomes longer, suggesting that a copper-rich layer forms on the electrode-posits that blocks the displacement reaction. The displacement reaction can be minimized by lowering the Cu + concentration at the electrode surface through the application of a superimposed current during t off whose magnitude is comparable to that of the limiting current for Cu + .

The reactions occurring at potentials of the second reduction wave of diethyl fumarate (DEF) in dimethylformamid e solutions, where a current dip is frequently observed in the voltammograms in the absence of added proton donors, was investigated, The over-all reaction order was determined by rotating disk electrode studies of the variation in the current at the dip with DEF concentration and theoretical results obtained by digital simulations, Analysis of products of macroscale electrolyses by NMR and mass spectroscopy was also undertaken. Several mechanisms are considered and one in which the electrogenerated dianion is protonated by the parent DEF to produce a carbanion which can initiate formation of dimeric and trimeric species is proposed.

The photo-Kolbe reaction (electro-oxidation of acetate) on TiO2 in aqueous solution has been studied by means of a rotating ring-disk electrode (RRDE) with a TiO2 disk and Pt ring. The oxidation of acetate competes very efficiently with water for photogenerated holes on the illuminated n-TiO2 disk as shown by a decrease in the collection efficiency for oxygen reduction. No oxidation product of acetate was detected on the ring. Competitive oxidation of iodide with acetate and water was also investigated. Equations for determining relative rate constants for competitive reactions are derived and the applicability of the RRDE in studying such systems discussed.

Determination de la constante de vitesse d'une reaction homogene entre le cuivre(I) et le fer (III) en solution acide. Etude theorique de la reduction chimique du fer(III) en fonction de la concentration de l'acide. La vitesse de balayage du potentiel est de 3mV/s et la rotation de l'electrode de 400 t/mn

The rotating ring-disk electrode method has been applied to study several new aspects of the oxidation mechanism of cadmium in concentrated potassium hydroxide solutions

The photo‐oxidation mechanisms of methanol, formaldehyde, and formic acid, which are potentially "current‐doubling agents," were investigated using the RRDE technique. The disk electrode was and was illuminated by a xenon lamp while the ring electrode was Pt. Hydrogen ion, generated at the disk during the oxidation of water or the organic solute, was observed by its reduction near −1V vs.. SCE at the ring. Formic acid was also reduced to hydrogen at the ring electrode in this potential region. , produced by decomposition while in transit from the disk, was reduced at −0.4V vs. SCE at the ring. The experimental results are consistent with initial production of hydroxyl radicals by photogenerated holes, followed by oxidation of the organic solute. One pathway involves injection of an electron into the conduction band resulting in increased photocurrents. Although true current‐doubling (100% increase) was not observed, photocurrent increases of ~50% were observed.

The reduction of the diactivated olefins dimethyl fumarate (DMeF), diethyl fumarate (DEF), di-n-butyl fumarate (DBF), dimethyl maleate (DMM), diethyl maleate (DEM), and di-n-butyl maleate (DBM), in N,N-dimethylform amidetetra-n-butylamm onium iodide solutions saturated with disso]ved carbon dioxide at a platinum electrode has been studied by rotating ring-disk electrode and cyclic voltammetry and in situ electron spin resonance spectroscopy. The results indicate that the rate-determining step for each compound is the reaction of the radical anion with CO2; the radical anions are also involved in the dimerization and (for maleates) isomerization reactions which occur in the absence of CO2. The coupling of the carboxylated radical to dimeric carboxylate is rapid. The rate constants for the reaction of the radical anions with CO2 were faster for maleates than for fumarates; pseudo-first order rate constants for a saturated CO2 solution (ca. 0.2M) are DMeF, 1.5 sec-1; DEF, {].47 sec-1; DBF, 0.35 sec-1; DMM, 32.0 sec-~; DEM, 19.4 sec-1; and DBM, 18.0 sec-L

Etude theorique de la cinetique de diffusion a une electrode tournante disque anneau. Deux cas sont envisages: transfert d'electron au disque, reaction chimique en solution, transfert d'electron a l'anneau ou bien transfert d'electron a l'anneau, reaction chimique en solution, transfert d'electron au disque

The degradation reaction kinetics of oxidized polyaniline has been studied employing rotating ring-disk electrode techniques. Polyaniline films were grown on the disk electrode and were then oxidized at a potential more positive than 0.90V vs. Ag/AgC1, while the degradation product (benzoquinone) was monitored at the ring electrode at an applied potential of 0.05V. The product was monitored either with the disk potential maintained at >0.90V (closed-circuit experiment) or with the disk circuit disconnected after the polyaniline film was oxidized for some time (open-circuit experiment). The results of closed-circuit experiments indicate that electrochemical generation of oxidized polyaniline was a limiting step and its rate decayed for a given amount of polyaniline film according to the zeroth order. The rate of hydrolysis for the oxidized polyaniline in quinonoid forms was determined to be consecutive first order from open-circuit experiments. The dependencies of the hydrolysis reaction on the acidity of the degradation medium and sulfate concentrations have also been studied; the results are consistent with the Schiff base hydrolysis mechanism.

Competition reactions at ..cap alpha..-Fe/sub 2/O/sub 3/ photoanodes were studied using the RRDE technique. It was found that iodide, bromide, and chloride ions were photo-oxidized in preference to water in acidic solutions. The competition ratio was measured as a function of halide-ion concentration, halide-ion flux, light intensity, electrode potential, and solution pH. A direct correlation between the disk photocurrent and the competition ratio at a given halide flux was demonstrated. A lack in selectivity for the dark current was also observed.

Etude de l'electrodissolution de l'alliage a diverses vitesses de rotation, divers potentiels et diverses concentrations de Cl − et H +

Demonstration des possibilites d'application de la voltammetrie de redissolution avec une electrode disque-anneau tournant a l'etude du depot electrolytique d'alliages Ni-Fe

The reduction of the activated olefins dimethyl fumarate, cinnamonitrile, and fumaronitrile in tetra‐n‐butylammonium iodide‐dimethylformamide solutions at a platinum electrode has been studied by rotating ring‐disk electrode (RRDE) voltammetry, cyclic voltammetry, and coulometry. The results indicate that each compound undergoes a one‐electron reduction to the anion radical which then undergoes a dimerization reaction. Rate constants for this dimerization reaction were found to be 110 (dimethyl fumarate), 880 (cinnamonitrile), and . Evidence of some bulk polymerization reaction was obtained from the coulometric results.